In accordance with a recent automobile technology, in order to decrease an amount of use of a fossil fuel, a research into an environment-friendly field using electricity as a power source has been gradually increased. As a result of the above mentioned research, an electric automobile only using electricity as the power source, a hybrid automobile appropriately using the fossil fuel and electricity together with each other, and the like have been commercialized. The above-mentioned electric automobile or hybrid automobile is generally provided with a battery such as a secondary battery as the power source for stably supplying electricity.
The battery generally produces power using an electrochemical reaction and includes a cell in which an actual reaction takes place, a case having a plurality of cells stacked therein and supporting the plurality of cells, and the like. Particularly, in order to use the above-mentioned battery in the automobile, high capacity is required. Therefore, the battery which is packaged by gathering a plurality of unit cells and formed in a form of a high capacity battery pack has been widely used for the automobile.
Meanwhile, in most cases, since the automobile is parked outside, it has a very large change range of its usage condition, for example, it is largely affected by a change between winter and summer seasons, a change between day and light, a weather change, and the like, heating values from the respective components are significantly changed according to driving conditions such as when the automobile is being driven and is stopped, and the like. As a result, phenomenon that moisture such as rainwater is permeated into an interior of the automobile, the moisture is condensed and formed at any portion inside the automobile, or the like is necessarily caused. It is apparent in most machinery that the moisture adversely affects lifespan of many parts, operation flexibility of an apparatus, and the like. Particularly, since the battery pack is a part directly producing power, it has a problem that power production efficiency is decreased when the moisture is permeated and further problem of electrical shot possibility, or the like.
As described above, dangerousness caused by the moisture in the battery pack is very significant. However, because of the usage conditions changed depending on an external environment, an automobile driving condition, or the like as described above, it may not be excluded that the moisture is unavoidably formed in the battery pack. Therefore, the battery pack is generally provided with a drainage system for draining the moisture collected inside the battery pack by being produced from the interior of the battery pack or being introduced from the outside.
A drainage system of the battery pack which is widely used according to the related art has a hole formed in a bottom surface of a case of the battery pack and a cap inserted into the hole from the outside of the bottom surface of the case of the battery pack. In this case, the cap is formed to be connected to a bottom surface of the automobile by a spring and receives force pushed by elastic force of the spring to thereby be stably inserted and supported into the hole. In this case, in the case in which the bottom of the battery pack is filled with water to some degree, weight of water becomes large the elastic force of the spring, such that the cap is pushed. As a result, if the hole is opened, then the water collected on the bottom of the battery pack may be discharged through the hole.
However, in a case of the drainage system according to the related art as described above, there was a problem that in the case in which the water of a predetermined amount or more is not collected on the bottom of the battery pack, the drainage is not performed. As such, even in a case of a small amount of water, that is, even if the amount is a small amount enough not to contact a battery system inside the battery pack, if the small amount of water is collected on the bottom of the battery pack, the water may be sloshed due to vibration and impact by the automobile driving and adversely affect the battery system.
Several technologies for easily performing the drainage in a cell field have been disclosed. Particularly, technologies enabling the drainage to be performed by several structures using buoyancy have been variously disclosed in Korean Patent Laid-Open Publication No. 2011-0075542 entitled “Water-Trap Apparatus of Fuel Cell System”, Korean Patent Laid-Open Publication No. 2011-0023224 entitled “Water Trap Device of Fuel Cell System”, Korean Patent Laid-Open Publication No. 2011-0017591 entitled “Water Drain Device for Exhaust Manifold of Fuel Cell System”, and the like. However, because the related arts as described above also have a structure in which the drainage may be performed only in the case in which the water of a predetermined amount or more is collected, they do not at all solve the problems of the drainage system of the battery pack according to the related art as described above. In addition, the apparatus of the above-mentioned related arts has a large volume of the drainage system itself, many numbers of components, a complex structure, and the like as compared to the drainage system of the battery pack according to the related art, such that an installation position thereof may be limited and production cost may be expensive.